Pre-filled hypodermic syringes can be used for home-use because they may be prepared with a required dosage of a pharmaceutical product and are operated by merely advancing the stopper of the syringe. Aside from the costs of the particular medication used, pre-filled syringes may be economically manufactured.
Nevertheless, pre-filled syringes can have drawbacks. Specifically, many users are either frightened by an exposed injection needle or feel they are inherently incapable of performing an injection. Because of aversions to exposed needles, as well as health and safety issues that may be involved, various types of injectors and other devices have been developed for concealing needles from the user and automating the injection task to assist the user in performing the injection, ensure reliable delivery of the medication and ensure patient safety. See the following patents or patent applications, which are each herein incorporated by reference in its entirety: U.S. Pat. Nos. 8,052,645 and 8,177,749; U.S. Publ. No. 2012/0101439; and PCT Publ. No. WO 2012/145685.
Typically, three tasks may be performed when injecting a drug into a patient with a hypodermic syringe: 1) insertion of the needle into the patient; 2) injection of the drug from the syringe into the patient; and 3) withdrawal of the needle after the injection has been completed. For each task, the magnitude and direction of forces on the syringe, as well as the location of their application, may be different from the other tasks. For example, insertion of the needle may require the application of a minimal force on the syringe, for a very short period of time. On the other hand, injection of the medicament may require the application of a much greater force on the plunger of the syringe, and this force may need to be applied for a relatively longer period of time. Further, needle withdrawal may require the application of a force in an opposite direction from needle insertion. These, and other similar considerations, may become relevant when the injection process is to be automated.
In addition to these mechanical considerations, the design of an autoinjector may require user-friendly considerations. In particular, it may be desirable for the injection needle of the syringe to be operationally concealed from the view of a user. Preferably, this concealment is maintained before, during and after an injection procedure. Further, it may be desirable that operation of the syringe be limited to only those times when the syringe is properly positioned for an injection and/or when the appropriate sequence of actions are performed by the user.
Accordingly, an improved autoinjector apparatus is needed.